US20020144671A1 - Cylinder injection type internal combustion engine, control method for internal combustion engine, and fuel injection valve - Google Patents

Abstract

There is provided a cylinder injection type internal combustion engine capable of performing stratified charge operation at the time of a vehicle speed of 120 km/h and/or an engine rotational speed of 3200 rpm to enhance the fuel efficiency and/or to observe the emission regulations. In the internal combustion engine, a stratum of air and/or air flow is formed between a fuel spray injected from an injection valve and the top face of a piston and/or the wall surface of a combustion chamber, and a face shape contrived to guide the air flow is formed on the top face of the piston.

Also, the stratified charge operation can be performed even at the time of cold start or cranking.

Description

TECHNICAL FIELD
• The present invention relates to a cylinder injection type internal combustion engine in which fuel is injected directly into a combustion chamber of an internal combustion engine, a control method for an internal combustion engine, and a fuel injection valve.[0001]
BACKGROUND ART
• In a conventional internal combustion engine of this type, a projecting portion is formed in the center on top face of a piston to form a depression called a cavity in the piston. Thereupon, fuel is injected from a fuel injection valve toward this cavity in the piston at the second half stage of the compression stroke of the internal combustion engine, so that a fuel spray repelled by the cavity is concentrated in the direction of ignition plug (Society of Automotive Engineers of Japan Annual Proceedings 976, Paper No. 9740307, October, 1997).[0002]
• Thus, the stratification of fuel in the combustion chamber is achieved, and combustion can be produced even with a lean mixture of an air-fuel ratio of about 40. Usually, such a combustion process is referred to as a stratified charge lean burn operation, which serves for reducing fuel consumption at the time of low-load operation of the internal combustion engine.[0003]
• Also, JP-A-7-119507 has disclosed a combustion system in which at the time of high-load operation, the operation is switched to a so-called homogeneous operation in which fuel is injected during the intake stroke so that the fuel is distributed uniformly in the whole of the combustion chamber.[0004]
• Further, JP-A-6-81656, JP-A-10-110660, JP-A-7-293259, JP-A-10-30441, JP-A-10-169447, and JP-A-10-896, and U.S. Pat. No. 5,850,816 have disclosed a combustion system in which a tumble air flow is produced in the combustion chamber, and a fuel spray is concentrated around the ignition plug by this tumble air flow.[0005]
• However, even if any of the above-described combustion systems is used, most of fuel injected from the injection valve sticks to the piston and the wall surface in the combustion chamber, so that there are limitations in increasing fuel efficiency and reducing harmful components (for example, hydrocarbon) in exhaust gas due to the stratified charge operation.[0006]
• Also, the stratified charge operation cannot be provided under a condition of 80 km/h or 2400 rpm and higher.[0007]
• A first object of the present invention is to reduce fuel sticking to the piston and the wall surface in the combustion chamber and to decrease HC in exhaust gas.[0008]
• A second object of the present invention is to increase the output at the time of homogeneous operation.[0009]
• A third object of the present invention is to provide a fuel injection valve for cylinder injection, in which less fuel sticks to the piston.[0010]
• A fourth object of the present invention is to enable the stratified charge operation even at a vehicle speed of 80 km/h and higher or at an engine rotational speed of 2400 rpm and higher (for example, in a high speed region where the vehicle speed is 120 km/h or the engine rotational speed is 3200 rpm).[0011]
DISCLOSURE OF THE INVENTION
• The above first object is attained by a cylinder injection type internal combustion engine comprising a combustion chamber into which air is sucked; a fuel injection valve for injecting fuel directly into the combustion chamber; and a piston for changing the volume of the combustion chamber, whose central portion of top face is equal in height to or lower than the surroundings, characterized in that a stratum of the sucked air or a stratum of air flow is interposed between a fuel spray injected from the fuel injection valve and the piston.[0012]
• Also, the above first object is attained by a cylinder injection type internal combustion engine comprising a fuel injection valve for injecting fuel directly into a combustion chamber of the internal combustion engine, characterized in that penetration of a fuel spray injected from the fuel injection valve into the combustion chamber is set to be shorter than a distance between the top face of a piston reciprocating in the combustion chamber and a fuel discharge port of the fuel injection valve during a period of time from the start of injection to the completion of injection of fuel.[0013]
• Also, the above first object is attained by a cylinder injection type internal combustion engine comprising a fuel injection valve for injecting fuel directly into a combustion chamber of the internal combustion engine, the fuel injection valve being formed so that the penetration of a fuel spray 3.8 msec after the injection of fuel to the atmosphere of the atmospheric pressure is 60 mm or shorter.[0014]
• Also, the above first object is attained by a cylinder injection type internal combustion engine comprising a fuel injection valve for injecting fuel directly into a combustion chamber of the internal combustion engine, the fuel injection valve being formed so that a fuel spray with a Zauter mean particle size of 20 μm or smaller is injected.[0015]
• Also, the above first object is attained by a cylinder injection type internal combustion engine, comprising a combustion chamber for the internal combustion engine into which air is sucked through an intake valve; a fuel injection valve for injecting fuel directly into the combustion chamber; swirl flow generating means for generating an air flow in the combustion chamber; and operation condition detecting means for detecting the operation condition of the internal combustion engine, the internal combustion engine having a control unit for supplying a fuel injection valve driving signal to the fuel injection valve so that fuel is injected at the second half stage of the compression stroke when the detected operation condition is at a low load.[0016]
• Also, the above second object is attained by a cylinder injection type internal combustion engine comprising a combustion chamber of the internal combustion engine, into which air is sucked through an intake valve; a fuel injection valve for injecting fuel directly into the combustion chamber; swirl flow generating means for generating a swirl air flow in the combustion chamber; and operation condition detecting means for detecting the operation condition of the internal combustion engine, the internal combustion engine having a control unit for supplying a fuel injection valve driving signal to the fuel injection valve so that fuel is injected on the intake stroke when the detected operation condition is at a medium load.[0017]
• Also, the above second object is attained by a cylinder injection type internal combustion engine comprising a combustion chamber of the internal combustion engine, into which air is sucked through an intake valve; a fuel injection valve for injecting fuel directly into the combustion chamber; and operation condition detecting means for detecting the operation condition of the internal combustion engine, the internal combustion engine having a control unit for supplying a fuel injection valve driving signal to the fuel injection valve so that fuel is injected for a period of time when the intake air velocity is lower than the spray velocity on the intake stroke when the detected operation condition is at a high load.[0018]
• Also, the above second object is attained by a cylinder injection type internal combustion engine comprising an upstream swirl type fuel injection valve for injecting fuel directly into a combustion chamber of the internal combustion engine; and operation condition detecting means for detecting the operation condition of the internal combustion engine, the internal combustion engine having a control unit for supplying a fuel injection valve driving signal to the fuel injection valve so that fuel is injected at a time for a period of time when the intake air velocity is higher than the spray velocity on the intake stroke when the detected operation condition is at a high load.[0019]
• Also, the above first object is attained by a control method for a cylinder injection type internal combustion engine, in which when the operation condition of the internal combustion engine is at a low load, a swirl air flow is generated in a combustion chamber, fuel is injected at the first half stage of the compression stroke, and a rich mixture stratum is formed inside the swirl air flow, whereby stratified charge lean operation is performed.[0020]
• Also, the above second object is attained by a control method for a cylinder injection type internal combustion engine, in which when the operation condition of the internal combustion engine is at a medium load, a swirl air flow is generated in a combustion chamber, fuel is injected on the intake stroke, and a mixture with a homogeneous concentration is generated in the combustion chamber by the swirl air flow, whereby homogeneous lean operation is performed.[0021]
• Also, the above second object is attained by a control method for a cylinder injection type internal combustion engine, in which when the operation condition of the internal combustion engine is at a high load, fuel having an amount capable of achieving a stoichiometric air-fuel ratio is injected for a period of time when the intake air velocity is lower than the spray velocity on the intake stroke, and a mixture with a homogeneous concentration is generated in the combustion chamber by intake air, whereby homogeneous stoichiometric operation is performed.[0022]
• Also, the above third object is attained by a fuel injection valve for injecting fuel directly into a combustion chamber of an internal combustion engine, characterized in that a fuel spray injected from the fuel injection valve has a penetration of 60 mm or shorter 3.8 msec after the time when fuel is injected to the atmosphere of the atmospheric pressure.[0023]
• Also, the above third object is attained by a fuel injection valve for injecting fuel directly into a combustion chamber of an internal combustion engine, characterized in that the spray particle size of fuel injected from the fuel injection valve is 20 μm or smaller in terms of Zauter mean particle size.[0024]
• Further, the above fourth object is attained by a cylinder injection type internal combustion engine comprising a combustion chamber into which air is sucked; a fuel injection valve for injecting fuel directly into the combustion chamber; and a piston for changing the volume of the combustion chamber, characterized in that an air flow is generated in the combustion chamber to form a stratum of the sucked air or a stratum of air flow between a fuel spray injected from the fuel injection valve and the piston, and a guide face for guiding the flow on the top face of piston to a position just under the injection valve.[0025]
• Specifically, the object is attained by a cylinder injection type internal combustion engine comprising air flow generating means for generating a tumble air flow in a combustion chamber of the engine; a piston having a top face shape contrived so as to guide the air flow generated in the combustion chamber from the side distant from a fuel injection valve to a position just under the fuel injection valve along the top face of the piston; and the fuel injection valve for supplying a fuel spray to the outer stratum of the air flow extending from the fuel injection valve to an ignition plug.[0026]
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a schematic view showing an engine system;[0027]
• FIG. 2 is a block diagram (1);[0028]
• FIG. 3 is a block diagram (2);[0029]
• FIG. 4 is a view showing an operation region map;[0030]
• FIG. 5 is a view showing a swirl flow in a combustion chamber;[0031]
• FIG. 6 is a view showing an installation position of a subsidiary intake air passage;[0032]
• FIG. 7 is a view showing a relationship between the subsidiary intake air passage and the swirl flow;[0033]
• FIG. 8 is a view showing a relationship between the injection direction and the swirl flow;[0034]
• FIG. 9 is a view showing another method for producing a swirl flow;[0035]
• FIG. 10 is a diagram showing a control method at the time of lean burn operation;[0036]
• FIG. 11 is a diagram showing fuel spray characteristics;[0037]
• FIG. 12 is a view showing the outline of the observation result of spray behavior;[0038]
• FIG. 13 is a diagram showing a relationship between intake air velocity and injection pulse at the time of full-open operation;[0039]
• FIG. 14 is a view showing a comparison between single injection and divided injection;[0040]
• FIG. 15 is a diagram showing a relationship between the intensity of swirl flow and the injection pulse;[0041]
• FIG. 16 is a diagram showing a relationship between intake air velocity and injection pulse at the time of full-open operation;[0042]
• FIG. 17 is a block diagram of a four-hole diffusion type nozzle;[0043]
• FIG. 18 is a block diagram of a hole position shifting type nozzle;[0044]
• FIG. 19 is a block diagram of a multi-hole type nozzle;[0045]
• FIG. 20 is a block diagram of a flow path change type nozzle;[0046]
• FIG. 21 is a block diagram of a fuel swirl type nozzle having square holes;[0047]
• FIG. 22 is a block diagram of a fuel swirl type nozzle having round holes;[0048]
• FIG. 23 is a block diagram of a slit type nozzle;[0049]
• FIG. 24 is a block diagram of a four-hole slit type nozzle;[0050]
• FIG. 25 is a block diagram of another four-hole slit type nozzle;[0051]
• FIG. 26 is a block diagram of a two-hole slit type nozzle;[0052]
• FIG. 27 is a block diagram of a four-hole independent swirl type nozzle;[0053]
• FIG. 28 is a block diagram of a four-hole collision type nozzle;[0054]
• FIG. 29 is a block diagram of an eight-hole collision type nozzle;[0055]
• FIG. 30 is a block diagram of a spray resonance type nozzle;[0056]
• FIG. 31 is a block diagram of another spray resonance type nozzle;[0057]
• FIG. 32 is a block diagram of a flow path change type nozzle;[0058]
• FIG. 33 is a perspective view showing an engine configuration in accordance with the embodiment;[0059]
• FIG. 34 is a view showing one example (long subsidiary intake air passage) of air flow generating means, FIG. 34([0060]a) being a top view, and FIG. 34(b) being a side view;
• FIG. 35 is a view showing one example (short subsidiary intake air passage) of air flow generating means, FIG. 35([0061]a) being a top view, and FIG. 35(b) being a side view;
• FIG. 36 is a view showing one example (notched valve) of air flow generating means, FIG. 36([0062]a) being a top view, and FIG. 36(b) being a side view;
• FIG. 37 is a view showing one example (notched valve+gate valve) of air flow generating means, FIG. 37([0063]a) being a top view, and FIG. 37(b) being a side view;
• FIG. 38 is a graph showing a comparison of tumble ratios of air flow generating means;[0064]
• FIG. 39 is a perspective view showing an air flow in a combustion chamber in the case of flat piston;[0065]
• FIG. 40 is a perspective view showing a shape of an improved piston;[0066]
• FIG. 41 is a schematic view showing a transfer behavior of fuel spray in accordance with the embodiment;[0067]
• FIG. 42 is a side view showing a relationship between engine shape and fuel spray;[0068]
• FIG. 43 is a graph showing a relationship between top end angle under a pressurized condition and engine performance;[0069]
• FIG. 44 is an explanatory view for definition of injection angle;[0070]
• FIG. 45 is a view showing a configuration of an impulse swirl meter;[0071]
• FIG. 46 is a perspective view showing one example of a direct injection type engine using the present invention; and[0072]
• FIG. 47 is a schematic view in which FIG. 46 is viewed from above the combustion chamber.[0073]
BEST MODE FOR CARRYING OUT THE INVENTION
• Embodiments of the present invention will be described with reference to the accompanying drawings.[0074]
• FIG. 1 shows one example of an engine system to which the present invention is applied. An[0075]engine11 has a crank mechanism comprising of a connectingrod14 and acrankshaft15, and acombustion chamber13 is formed by apiston12 connected to the crank mechanism and an engine head of theengine11. Thecombustion chamber13 is sealed byintake valves27,exhaust valves29, anignition plug28, and afuel injection valve26 which are installed on the engine head.
• In the[0076]engine11, air necessary for combustion is sucked into thecombustion chamber13 by the reciprocating motion of thepiston12. Dirt and dust contained in the air to be sucked are removed by anair cleaner18, and an intake air amount, which is a basis for calculating a fuel injection amount, is measured by anair flow sensor19. The intake air amount is controlled by the degree of opening of athrottle valve20, and the air to be sucked passes through a mainintake air passage21 and a subsidiaryintake air passage22 according to the operation condition of theengine11. Acontrol unit36 for controlling theengine11 is supplied with a crank angle signal sent fromcrank angle sensors16 and17 and an acceleration stroke sent from an accelerator position sensor38. Besides, as shown in FIG. 2, thecontrol unit36 is supplied with various pieces of information such as an intake air amount signal sent from theair flow sensor19, an A/F signal sent from an air-fuel ratio sensor31 installed in an exhaust pipe, and an exhaust catalyst temperature signal sent from atemperature sensor32.
• The[0077]control unit36 detects the operation condition of theengine11 based on the information such as the crank angle signal and acceleration stroke, and determines the fuel injection amount, injection timing, and ignition timing based on the operation condition. Anignition coil34 generates a high voltage according to an ignition signal sent from thecontrol unit36, and produces an ignition spark by means of theignition plug28. A fuel injectionvalve drive unit35 amplifies an injection signal sent from thecontrol unit36 to drive thefuel injection valve26. Fuel is supplied from a high-pressure fuel pump24, which is driven by theengine11, to thefuel injection valve26 through afuel pipe25.
• In order to form a necessary swirl flow in the[0078]combustion chamber13 according to the operation condition of theengine11, the degree of opening of aflow dividing valve23 in the mainintake air passage21 is controlled to regulate the amount of air introduced from the subsidiaryintake air passage22. To open and close the flow dividing valve, a flow dividing valve driving signal VD is sent from thecontrol unit36 according to the operation condition of the engine. The air passing through the subsidiaryintake air passage22 has a high speed and directivity, so that it forms a necessary swirl flow in thecombustion chamber13. By opening theflow dividing valve23, air flows through the mainintake air passage21, and the air passing through the subsidiaryintake air passage22 lessens. Thereby, the intensity of the swirl flow formed in thecombustion chamber13 is regulated.
• FIGS. 2 and 3 are block diagrams showing the flow of control signals. The flow of control signals in the[0079]engine control unit36 will be described with reference to these figures.
• In[0080]block361, the crank angle signal, the acceleration stroke θ_α, etc. are taken and held, an engine rotational speed Ne is calculated from the crank angle signal, and a target torque T of the engine is calculated from the acceleration stroke θ_α and the engine rotational speed Ne. In blocks362,363 and364, a fuel injection pulse width Tp, fuel injection start timing IT, and ignition timing θ_Adare determined from the engine rotational speed and the target torque held in theblock361. The fuel injection amount is substantially proportional to the fuel injection pulse width Tp. The fuel injection pulse width Tp and the fuel injection start timing IT are, as shown in FIG. 4, determined from a map of the engine rotational speed Ne and the target torque T. Signals (fuel injection valve drive signals) of the fuel injection pulse width Tp and the injection start timing IT are sent to the fuel injectionvalve drive unit35. Also, inblock364, the ignition timing is determined according to the operation condition of the engine, and a signal of the ignition timing is sent to theignition coil34. The fuel injection start timing IT is, as shown in FIG. 10, determined during the intake stroke and the compression stroke according to the operation condition of the engine so as to correspond to the combustion system of each operation condition, and the number of injections N_I, is also determined (four times in FIG. 15). That is to say, the combustion method (combination of Tp, IT, θ_Ad, etc.) in thecombustion chamber13 is changed in response to the operation condition.
• In a low-load region A (running at a constant speed of 60 km/h, for example), a strong swirl flow is produced (the[0081]flow dividing valve23 is fully closed) in thecombustion chamber13, and also fuel is injected at the second half stage of the compression stroke, by which the stratified charge lean operation with an air-fuel ratio of about 40 is performed.
• In a medium-load region B (running at a constant speed of 100 km/h, for example, or slight acceleration from the region A), a weak swirl flow is produced (the[0082]flow dividing valve23 is half opened) in thecombustion chamber13, and also fuel is injected on the intake stroke, by which the stratified charge lean operation with an air-fuel ratio of about 20 to 25 is performed.
• In a high-load region C (running at a constant speed of over 120 km/h, for example, or slow acceleration from the region A), no swirl flow is produced (the[0083]flow dividing valve23 is fully opened) in thecombustion chamber13, and fuel is injected on the intake stroke, by which the homogeneous operation with an air-fuel ratio of about 14.7 is performed.
• In a region D of further high rotation and high load (running at a constant speed of 140 km/h, for example, or quick acceleration from the region A), the air-fuel ratio is made lower than 14.7.[0084]
• The intensity of swirl flow includes a strong swirl flow, no swirl flow, and a weak swirl flow having an intermediate intensity therebetween.[0085]
• Next, the method for lean burn operation performed in the regions A and B will be described with reference to FIG. 5.[0086]
• FIG. 5 shows a relationship between the swirl flow and the injected fuel spray. A[0087]swirl flow40 generated by the mainintake air passage21, the subsidiaryintake air passage22, and theflow dividing valve23 forms a transverse swirl flow in thecombustion chamber13.
• FIG. 6 shows the installation position of the subsidiary[0088]intake air passage22.
• FIG. 6([0089]a) shows arange21ain which the subsidiaryintake air passage22 can be installed. To provide an intake air resistance at the time of high load (C, D), the subsidiary intake air passage should preferably be installed so as to be closer to the edge of the mainintake air passage21. For this reason, the subsidiary intake air passage is installed in a range on the outside of the axis of astem27aof theintake valve27.
• FIG. 6([0090]b) shows an installation method in the case where the mainintake air passage21 is divided into two portions. The subsidiaryintake air passage22 is provided at one portion of the mainintake air passage21, and the opening thereof is directed into thecombustion chamber13, by which a swirl flow as denoted by anarrow mark40 is produced.
• FIG. 6([0091]c) shows an installation method in the case where the mainintake air passage21 is formed into one. The subsidiaryintake air passage22 is installed so as to be close to a tangential line at the outer periphery of thecombustion chamber13, and the opening thereof is directed along the wall surface in thecombustion chamber13, by which a swirl flow as denoted by anarrow mark40 is produced.
• FIG. 7([0092]a) shows a relationship between the subsidiaryintake air passage22 and theswirl flow40 produced in thecombustion chamber13. If an angle α of the subsidiaryintake air passage22 with respect to the horizontal plane is large, arotation axis40aof theswirl flow40 is tilted, with the result that theswirl flow40 is not a horizontal vortex, but becomes a vortex having a slantwise component. In this case, the fuel component concentrated in the center of the combustion chamber is shifted from the centerline of the combustion chamber by the tilt of the rotation axis of the swirl flow.
• FIG. 7([0093]b) shows a case where the tilt angle a of the subsidiaryintake air passage22 is small. In this case, the air passing through the subsidiaryintake air passage22 flows into the combustion chamber at an angle close to the horizontal, so that the tilt of rotation axis of the swirl flow can be decreased. Thereby, the fuel component concentrated in the center of the combustion chamber can be held until the second half stage of the compression stroke.
• FIG. 8([0094]a) shows a relationship between afuel spray41 and theswirl flow40. As an installation angle γ (angle with respect to the horizontal plane) of thefuel injection valve26 becomes larger, thefuel spray41 can be held in the center of the combustion chamber more easily. If thefuel injection valve26 is located at the installation position of theignition plug28, the fuel spray is surely held in the center of the combustion chamber. When the fuel injection valve is located under the intake valve as in this embodiment, it is thought that the fuel spray goes beyond theswirl flow40 and diffuses to the peripheral portion in the combustion chamber depending on the penetration of the spray. Therefore, a condition in which the fuel spray does not go beyond the swirl flow must be considered. This condition is described later.
• FIG. 8([0095]b) shows a method in which the injection direction of the fuel spray is deflected to prevent the diffusion of the fuel spray to the peripheral portion in the combustion chamber. Since afuel spray41ais injected so as to be tilted through an angle θ with respect to the installation angle γ of the fuel injection valve, the fuel spray is easily taken into theswirl flow41a. If the fuel spray is used together with a spray using an atomizer or a spray of short penetration shown in FIG. 14(b), the fuel spray can surely be held in the center of the combustion chamber.
• FIG. 9 shows another method for producing the swirl flow. The main[0096]intake air passage21 is divided into two passages, a main intake air passage provided with aflow dividing valve42 and a subsidiary intake air passage provided with a notchedvalve43, to communicate with the twointake valves27. Theflow dividing valve42 and the notchedvalve43 are connected to each other by one shaft so that the degree of opening of the valves can be regulated by the rotation of the shaft. When the valves are fully closed, air is introduced only through the intake air passage provided with the notched valve. Therefore, the flow velocity is increased, so that a strong swirl flow is formed in thecombustion chamber13. When the valves are fully opened, air is introduced through both the passages, so that the occurrence of the swirl flow is stopped. Although the main intake air passage and the subsidiary intake air passage are provided in FIG. 9, a construction without the subsidiary intake air passage is also possible.
• In both of the above-described two methods for producing the swirl flow, the air flow velocity in the vicinity of the cylinder wall surface of the[0097]combustion chamber13 is high, and that in the central portion is low. If fuel is injected after the first half stroke of the compression stroke (when the swirl flow is established), at which the swirl flow becomes strong, thefuel spray41 injected to the portion near the center of thecombustion chamber13 does not diffuse, and concentrates in the swirl flow. It is important that at this time, thefuel spray41 decelerates in the vicinity of the center of the combustion chamber, and does not arrive at the cylinder wall on the opposite side. For such a spray, the penetration thereof should preferably be 60 mm or less 3.8 msec after the fuel is injected to the atmosphere of the atmospheric pressure. Also, the spray particle size at this time should preferably be 20 μm or smaller in terms of Zauter mean particle size D32.
• The Zauter mean particle size is defined as a particle size calculated from the volume and the surface area when the spray particle is assumed to be a perfect sphere. It can easily be measured by using a measuring instrument such as a Phase Doppler Particle Analyzer (PDPA) or a Malvern particle analyzer. The numeral shown in the embodiment is the Zauter mean particle size measured at a[0098]position 50 mm below the nozzle tip.
• To obtain such fuel spray characteristics, an atomizer as shown in FIGS.[0099]17 to32 should preferably be used. The use of such an atomizer tends to weaken the penetrating force of spray. The atomizer itself will collectively be described later.
• The following is a description of a case where an atomizer is used.[0100]
• FIG. 10 shows a control method at the time of lean burn operation. The abscissas denote the crank angle of the engine for a period from the intake stroke to the compression stroke. The ordinates denote the intensity of the swirl flow produced in the combustion chamber. The swirl flow in the combustion chamber is affected by the degree of opening of the intake valve during the intake stroke, and becomes strongest in a period from the second half stage of the intake stroke to the first half stage of the compression stroke. Thereafter, the intensity of the swirl flow decreases.[0101]
• In the region A, because the stratified charge burn operation is performed, fuel is injected as denoted by a[0102]pulse51 when the swirl flow in the combustion chamber is established. The fuel injection amount and the injection timing are determined so that the exhaust amount of HC does not increase.
• In the region B, the homogeneous lean burn operation is performed. At this time, the air-fuel ratio is 20 to 25, and fuel is injected on the intake stroke as denoted by a[0103]pulse52 to reduce the exhaust amount of NOx. The fuel injected during the intake stroke is agitated by the swirl flow and is diffused in the combustion chamber, thereby being mixed uniformly.
• FIG. 11 shows the fuel spray characteristics for a cylinder injection engine. The abscissas denote the average particle size of spray, usually denoted in terms of the Zauter mean particle size D32. The ordinates denote the penetration or the spray arrival distance, denoting the spray length 3.8 ms after injection. The spray characteristics of an upstream swirling type injector widely used for a direct injection engine at present fall within a[0104]range55 by changing the fuel pressure, spray angle, and spray swirl force. With the use of an atomizer, the spray characteristics fall within arange56, which means that the particles are made fine. However, such a spray presents a problem in that the fuel spray is caused to flow to the intake air at the time of full-open output, so that the mixture becomes nonuniform.
• FIG. 12 shows the outline of the observation result of spray behavior in the combustion chamber of the engine. FIG. 12([0105]a) shows a case where the penetrating force of spray is strong, and FIG. 12(b) shows a case where the penetrating force of spray is weak. At the time of high load, the operation of the swirl flow generating means is stopped, that is, the flow dividing valve is opened fully. Thereby, the intake air amount is increased. Vertical swirl flows40aand40bare produced in thecombustion chamber13 by the flow passing through the upper side of the intake valve and the flow passing through the lower side thereof. The swirl flow40ais an air flow having passed through the upper side of the intake valve, and theswirl flow40bis a flow having passed through the lower side thereof. In the case shown in FIG. 12(a) where the penetrating force of spray is strong, the fuel spray is spread in the cylinder by the penetrating force of the spray itself, so that it is diffused uniformly in the cylinder by going with the flow of theair flow40a, by which satisfactory combustion can be provided. If such satisfactory combustion can be provided, the output can be taken out with a high efficiency with respect to the supplied fuel. However, in the case shown in FIG. 12(b) where the penetrating force of spray is weak, the fuel spray is caused to flow by the flow of theair flow40b,so that it cannot be diffused widely in the cylinder, by which a problem is caused in that the distribution of mixture becomes nonuniform (not homogeneous). Therefore, the injection timing is contrived as shown in FIG. 13.
• FIG. 13 shows a relationship between intake air velocity and injection pulse at the time of high load. The abscissas denote the crank angle of the engine on the intake stroke. The ordinates denote the approximate velocity of the intake air passing through the opened area of the intake valve. Since the opened area of the intake valve is first small, the velocity is high, and thereafter decreases. At the middle stage of the intake stroke, the intake air amount increases, so that the velocity increases again. Subsequently, the velocity decreases again, and increases before the intake valve is closed. Thereafter, the intake valve is closed. Since the charge efficiency in natural intake is about 70 to 80%, there is still a margin of intake, and the flow velocity is high even immediately before the intake valve is closed. In a spray with the spray characteristics using an atomizer denoted by the[0106]region56 in FIG. 11, the spray velocity is low (the penetrating force is weak), so that the spray is easily caused to flow by the intake air. If the spray velocity is higher than the intake air velocity, the spray is prevented from being caused to flow by the intake air flow. The spray velocity depends on the nozzle construction and the fuel pressure, and is independent of the engine rotational speed. Therefore, if fuel is injected at the above-described timing at which the intake air velocity changes and becomes lower than the spray velocity, the influence of the intake air on the spray can be reduced. Since the intake air velocity changes as denoted by acurve60, the period of time when the intake air velocity becomes lower than the spray velocity determined by the nozzle construction and the fuel pressure provides the injection allowable range. By carrying out control in this manner, the injected fuel can be prevented from being deflected, so that a homogeneous mixture can be formed. When the injection allowable range is narrow and a necessary amount of fuel cannot be injected at a time, fuel can be injected additionally as denoted byreference numeral61.
• The spray velocity is a velocity of fuel spray when the fuel spray is injected from the fuel injection valve into the atmospheric air. This spray velocity can be calculated by measuring the length from the tip end of the fuel injection valve to the tip end of the spray every unit time when the fuel spray is photographed by a high-speed camera. Also, the intake air velocity is a flow velocity of intake air when the intake air passes through the opening of the intake valve, and is changed by the degree of opening of the valve. Therefore, in order to measure the intake air velocity, a steady-state air flow is supplied to the engine head, and the degree of opening of the valve is changed, by which the intake air velocity is measured by using a hot wire flow velocity meter or the like.[0107]
• FIGS.[0108]14 to16 show the embodiment in which no atomizer is used and an upstream swirling type injector is used. This corresponds to a case where the penetrating force of spray is strong.
• FIG. 14([0109]a) shows a state in which a spray grows when fuel is injected by one injection using the upstream swirling type injector. The tip end portion of aspray41ais subjected to air resistance, and decelerates gradually. However, since the spray is injected continuously, the spray is carried away by the subsequently injected spray, so that the penetration becomes long. The penetration at this time is in the range of thespray characteristics55 shown in FIG. 11.
• FIG. 14([0110]b) shows a case where the same injection amount is injected at four times. The first injectedspray41ais subjected to air resistance and decelerates. The fuel is injected at multiple stages, so that the penetration becomes short because thespray41ais not carried away continuously. Subsequently injectedsprays41b,41cand41dare also subjected to the same operation, so that the penetration of the whole spray becomes shorter than the case where the fuel is injected at a time.
• FIG. 15 shows a relationship between the intensity of swirl flow in the combustion chamber and the injection pulse. In a region A where stratified charge combustion is produced, fuel is injected when the swirl flow is established. At this time, since the penetration is shortened by the divided injection, the fuel spray is contained in the swirl flow, so that it can be prevented from diffusing. In a region B where homogeneous lean operation is performed, fuel is injected before the swirl flow is established so that the injected fuel is mixed uniformly. At this time as well, the penetration is decreased by divided injection of fuel, whereby the fuel spray can be prevented from sticking to the piston and the cylinder wall.[0111]
• FIG. 16 shows a relationship between intake air velocity and injection pulse at the time of a high load (C, D). Since a stronger penetrating force of spray provides proper mixing with air at the time of a high load, the divided spray is stopped, and the injection timing is set as denoted by[0112]reference numeral71 so that the intake air amount is increased most by intake air cooling, whereby the output can be increased.
• As described above, by changing the combustion method in the[0113]combustion chamber13 according to the operation condition, a problem can be overcome in that fuel sticks to the piston and thereby the exhaust amount of HC is increased in the regions A and B where the lean burn operation is performed. Also, the mixture distribution in the combustion chamber is made uniform in the regions C and D where the homogeneous operation is performed, whereby the output can be increased. At this time, the penetration can be shortened by employing an atomizer or a divided injection. A stratum of air is formed between the shortened penetration and the top face of piston, thereby restraining the sticking of fuel. Also, if a stratum of air flow is positively formed on the top face of piston and on the wall surface in the combustion chamber by using the swirl flow, the sticking of fuel can be reduced further. By forming the stratum of air or the stratum of air flow in this manner, the adhesion of fuel to the piston can be reduced. As a result, unburned components of fuel can be reduced, and the cooling operation of piston can be decreased. The stratum of air flow is formed more easily when a flat piston without cavity is used than when a piston with cavity is used. Also, the fuel spray is atomized and is made liable to be affected by the swirl flow, by which the fuel spray can be maintained in the swirl flow to provide stable and proper combustion.
• When the[0114]engine control unit36 is supplied with intake air amount Q_aor intake pipe pressure P and air-fuel ratio A/F in addition to the crank angle signal and the acceleration stroke, feedback control can be carried out so that the air-fuel ratio A/F has a constant value (for example, 14.7) to control the engine torque so as to be the target torque. Also, when thecontrol unit36 is supplied with combustion chamber pressure or knock sensor signal, the occurrence of knocking is detected and can be used for the control of ignition timing. Also, if thecontrol unit36 is supplied with water temperature, control for delaying the ignition timing can be carried out to warm up the engine at an early time.
• FIGS.[0115]17 to32 show tip end shapes of a fuel injection valve using an atomizer comprising of a multilayer plate. The basic configuration comprises several thin plates with a thickness of 0.1 to 0.5 mm lapped on one another, each plate being machined as shown in the figures. A first layer of the multilayer plate has an operation such that fuel is spread transversely and the penetrating force of fuel is decreased. The shapes of holes in the plates of a second and subsequent layers serve for controlling the spray shape and for atomization. Also, one plate with a thickness of 1.0 to 1.5 mm is drilled from both sides by laser beam machining or electrical discharge machining, by which a fuel passage hole similar to the fuel passage hole extending from the top face of the multilayer plate to the side thereof can be formed.Reference numeral2 in the figures denotes a nozzle for the fuel injection valve, which has asingle hole1. To the tip end thereof is attached a multilayer plate of a variety of shapes.
• The material of the multilayer plate is preferably a stainless steel, and the several plates are preferably joined by welding. Also, as an alternative method, silicon wafers processed by etching can be joined with an adhesive to produce the multilayer plate.[0116]
• FIG. 17 shows a four-hole diffusion type multilayer plate. The fuel flowing out of the[0117]nozzle hole1 spreads transversely in anintermediate chamber5 formed in aplate3, and ejects fromejection holes6 formed in aplate4. Although the plate formed with four ejection holes is shown, two or more holes may be formed. The ejection holes have an angle denoted by anarrow mark7 so that fuel is ejected to the outside. Therefore, the ejected fuels do not collide with each other.
• FIG. 18 shows a hole position shifting type multilayer plate. The fuel flowing out of the[0118]nozzle hole1 spreads transversely in anintermediate chamber5 formed in aplate3, passes throughejection holes6 formed in aplate4, and ejects fromejection holes7 formed in aplate8. Although the plate formed with four ejection holes is shown, two or more holes may be formed. The ejection holes6 and7 are arranged so as to shift from each other, and the sum of the opening area thereof is determined so as to be equal to or smaller than the cross sectional area of thesingle hole1.
• FIG. 19 shows a multi-hole type multilayer plate. The fuel flowing out of the[0119]nozzle hole1 spreads transversely in anintermediate chamber5 formed in aplate3, and ejects fromejection holes6 formed in aplate4. Although the plate formed with twelve ejection holes is shown, two or more holes may be formed. Also, although theejection hole6 is formed in parallel with the nozzle axis, the ejection hole may be inclined.
• FIG. 20 shows a flow path change type multilayer plate. The fuel flowing out of the[0120]nozzle hole1 spreads transversely inintermediate chambers5 and6 formed inplates3 and4, respectively, and ejects fromejection holes7 formed in aplate8. Although the plate formed with four ejection holes is shown, two or more holes may be formed. The intermediate chamber formed in theplate4 has a shape denoted byreference numeral6, and the intermediate chamber formed in theplate3 has a shape such that projecting portions as denoted byreference numeral5 are added to the shape ofreference numeral6. The ejection holes7 formed in theplate8 are located at positions under the projecting portions, so that the fuel flowing out of thenozzle hole1 does not arrive at the ejection holes7 directly, and is ejected after the flow path is changed in theintermediate chambers5 and6. By changing the flow path in the intermediate chambers, turbulence energy is given to the fuel.
• In FIG. 21, the fuel flowing out of the[0121]nozzle hole1 spreads transversely in anintermediate chamber5 formed in aplate3, and ejects from square ejection holes6 formed in aplate4. In the case of this nozzle, the effect of fuel atomization is larger when the fuel flowing through thenozzle hole1 is swirled.
• In FIG. 22, the fuel flowing out of the[0122]nozzle hole1 spreads transversely in anintermediate chamber5 formed in aplate3, and ejects fromejection holes6 formed in aplate4. Although the plate formed with four ejection holes is shown, two or more holes may be formed. In the case of this nozzle as well, the effect of fuel atomization is larger when the fuel flowing through thenozzle hole1 is swirled.
• FIG. 23 shows a slit type multilayer plate. The fuel flowing out of the[0123]nozzle hole1 spreads transversely in anintermediate chamber5 formed in aplate3, passes through aslit6 formed in aplate4, and ejects from aslit7 formed in aplate8. The fuel flowing from theslit6 into theslit7 ejects after once spreading transversely in theslit7. Therefore, the ejected fuel spray has a very thin film shape. The crossing angle between the slits is preferably 90 degrees.
• FIG. 24 shows a four-hole slit type multilayer plate. This type was derived based on the same concept as that of the slit type shown in FIG. 12. The fuel flowing out of the[0124]nozzle hole1 spreads transversely in anintermediate chamber5 formed in aplate3, passes through fourslits6 formed in aplate4, and ejects from fourslits7 formed in aplate8. The fuel flowing from theslit6 into theslit7 ejects after once spreading transversely in theslit7. The crossing angle between the slits is preferably 90 degrees.
• FIG. 25 shows a four-hole slit type multilayer plate. The fuel flowing out of the[0125]nozzle hole1 spreads transversely in anintermediate chamber5 formed in aplate3, and ejects fromslits6 formed in aplate4. In case of this nozzle, the effect of fuel atomization is larger when the fuel flowing through thenozzle hole1 is swirled.
• FIG. 26 shows a two-hole slit type multilayer plate. This type was derived based on the same concept as that of the slit type shown in FIG. 12. The fuel flowing out of the[0126]nozzle hole1 spreads transversely in anintermediate chamber5 formed in aplate3, passes through aslit6 formed in aplate4, and ejects fromslits7 formed in aplate8. Since the fuel flowing from theslit6 into theslits7 ejects after once spreading transversely in theslit7, the ejected fuel spray from one slit has a very thin film shape. Therefore, as the whole spray, a spray with a thickness is formed. The crossing angle between the slits is preferably 90 degrees.
• FIG. 27 shows a four-hole independent swirl type multilayer plate. The fuel flowing out of the[0127]nozzle hole1 spreads transversely in anintermediate groove5 formed in aplate3, passes throughejection holes6 formed in aplate4 and swirlgroove7 formed in aplate8, and, after being given a swirling force, ejects from ejection holes10 formed in aplate9. Although the plate formed with four ejection holes is shown, two or more ejection holes may be formed.
• FIG. 28 shows a four-hole collision type multilayer plate. The fuel flowing out of the[0128]nozzle hole1 spreads transversely in anintermediate chamber5 formed in aplate3, and ejects fromejection holes6 formed in aplate4. Although the plate formed with four ejection holes is shown, two or more ejection holes may be formed. The ejection holes have an angle denoted by anarrow mark7 so that fuel is ejected to the inside. Therefore, the ejected fuels collide with each other in the vicinity of the tip end of nozzle.
• FIG. 29 shows an eight-hole collision type multilayer plate. The fuel flowing out of the[0129]nozzle hole1 spreads transversely in anintermediate groove5 formed in aplate3, and ejects fromejection holes6 formed in aplate4. Although the plate formed with eight ejection holes is shown, two or more ejection holes may be formed. The eight holes have an angle such that the ejected fuels collide with each other at apoint7.
• FIG. 30 shows a spray resonance type multilayer plate. The fuel flowing out of the[0130]nozzle hole1 spreads transversely in anintermediate chamber5 formed in aplate3, and ejects from anejection hole6 formed in aplate4. The fuel spreading transversely in theintermediate chamber5 and the fuel ejecting from theejection hole6 resonate, and turbulence energy is given to the fuel. The resonance wavelength changes depending on the size of the intermediate chamber.
• FIG. 31 also shows a spray resonance type multilayer plate. The fuel flowing out of the[0131]nozzle hole1 spreads transversely in anintermediate chamber6 formed in aplate4, and ejects from anejection hole7 formed in aplate8. Aplate3 is formed with a single hole with the same inside diameter as that of thenozzle hole1 to change a distance from a valve seat of the fuel injection valve to theintermediate chamber6. Thereby, the resonance frequency of the fuel spreading transversely and the fuel ejecting from theejection hole7 is changed.
• FIG. 32 shows a flow path change type multilayer plate. The fuel flowing out of the[0132]nozzle hole1 spreads transversely in anintermediate chamber5 formed in aplate3, passes through aslit6 formed in aplate4, and flows into anintermediate chamber7 formed in aplate8. Theintermediate chamber7 has a shape such that projectingportions7 are added to the shape of theintermediate chamber5. The fuel having passed through theslit6 is divided into two flows, a flow along the outer periphery of theintermediate chamber7 and a flow along the projecting portion from the center. By these two flows, the fuel is swirled near the inlets of ejection holes10 formed in aplate9.
• In the above-described embodiment, the thickness of the[0133]plates3,4,8 and9 may be about 0.1 to 0.3 mm.
• As the system for atomization, a thin film atomization system, a collision atomization system, a swirl atomization system, and an atomization system utilizing turbulence are available. In FIGS.[0134]23 to26, the thin film atomization system is used, in FIGS. 28 and 29, the collision atomization system is used, in FIGS.20 to22,27, and32, the swirl atomization system is used, and in FIGS.17 to19,30, and31, the atomization system utilizing turbulence is used.
• Another embodiment of the present invention will be described below with reference to FIG. 33 and the following drawings.[0135]
• FIG. 33 is a block diagram of another embodiment. FIG. 33 is a perspective view of an engine in accordance with the embodiment. The main components include a notched[0136]valve43, serving as air flow generating means for generating air flow in acombustion chamber13, ashaft43a,apartitioning plate44, afuel injection valve26 for injecting fuel into thecombustion chamber13, and apiston12 having a top face shape such that a sufficient tumble strength can be provided. At the upper part of thecombustion chamber13, that is, on the side opposite to thepiston12, twointake valves27, twoexhaust valves29, anignition plug28, and afuel injection valve26 are provided. For thecombustion chamber13 formed by these elements, the volume thereof is changed by the reciprocating motion of thepiston12. When thepiston12 lowers with theintake valves27 being opened, air is sucked throughintake ports21. The amount of air sucked into thecombustion chamber13 is measured by an air amount sensor (not shown), and the amount of fuel injected from thefuel injection valve28 is determined based on the measured value. Twointake valves27 are provided to increase the amount of intake air. Theintake ports21 form flow paths communicating with the twointake valves27. Thefuel injection valve26 is installed between these flow paths, that is, between the twointake valves27.Reference numeral14adenotes a crankshaft of an engine, which shows an example for a four-cylinder engine.Reference numeral14bdenotes the axis of thecrankshaft14a,and14cdenotes the axis of a piston pin of thepiston12. Thefuel injection valve26 is installed so that the axis thereof is perpendicular to theaxis14cof the piston pin or theaxis14bof the crankshaft. The axis of thefuel injection valve26 is inclined toward a lower portion of theignition plug28, which is installed at the upper part of thecombustion chamber13, so that fuel easily concentrates around theignition plug28. By this configuration, in injecting on the intake stroke, fuel can be distributed widely in thecombustion chamber13, and in injecting on the second half stage of the compression stroke, sprays can be concentrated easily in the direction of theignition plug28. A tumble flow concentrated in the combustion chamber turns to a stratum of air flow on thepiston12, producing an air wall. The fuel spray is conveyed in the direction of ignition plug by this air flow. Further, the fuel spray is prevented from sticking to the piston top face because it is guided by the air wall. This system is referred to as a tumble air guide system. The spray shape and the injection direction of the fuel spray are set so that the fuel spray easily reaches the periphery of a plug gap of theignition plug28.
• FIGS.[0137]34 to37 show configuration examples of tumble generating means. FIG. 34 shows a configuration in which a subsidiaryintake air passage22 is provided in theintake port21. When theintake valves27 are opened and thepiston12 lowers, air is sucked through theintake ports21 and the subsidiaryintake air passages22. Although not shown in the figure, by closing valves installed in theintake ports21, the air flow through theintake ports21 is weakened, and the air flow through the subsidiaryintake air passages22 is strengthened. Since the inside diameter of the subsidiaryintake air passage22 is set to be smaller than that of theintake port21, the flow velocity of air flowing through the subsidiaryintake air passage22 is high. The main flow of air flowing out of the subsidiaryintake air passage22, which is as denoted by anarrow mark40, has an influence on theambient air40c,generally forming a tumble flow.
• FIG. 35 shows a configuration in which the subsidiary[0138]intake air passage22 is provided in theintake port21, in which a case where the subsidiaryintake air passage22 is short is shown. In this case, the main flow of air going out of the subsidiaryintake air passage22 is as denoted byreference numeral40, and conveys theambient air40c,but aflow40dwhose velocity is relatively low is produced undesirably. As a result, the air flow has a poor directivity as compared with the case where the subsidiaryintake air passage22 is long, so that a tumble flow necessary for the tumble air guide system is not formed.
• FIG. 36 shows a configuration in which the notched[0139]valve43 is provided at an intermediate position of theintake port21. The notchedvalve43 is fixed to theshaft43apenetrating the intake port wall so as to be opened and closed by rotating theshaft43a.When the notchedvalve43 is closed, the passage of lower half of the opening of theintake port21 is closed. Thereby, the flow velocity of intake air is increased. The notchedvalve43ais inevitably located at a position distant from theintake valve27 because of the construction of the engine head. Therefore, although the main flow is as denoted byreference numeral40, the flow expands immediately after passing through the notchedvalve43, producing a flow denoted byreference numeral40d,so that the air flow has a poor directivity.
• FIG. 37 shows a configuration in which the notched[0140]valve43 is provided at an intermediate position of theintake port21, and thepartitioning plate44 is provided to prevent the diffusion of flow after the air flow passes through the notchedvalve43. By this configuration, the air passage is formed so as to be kept smaller than theintake port21 to a position near theintake valve27, so that the flow velocity of air is increased. The main flow, which is as denoted by anarrow mark40, has an influence on theambient air40c,generally forming a tumble flow. The notchedvalve43 is referred to as a tumble control valve.
• FIG. 38 shows a comparison result for the performance of tumble generating means. The tumble ratio denoted on the ordinate is defined by the number of vertical rotations of air flow during one reciprocating motion of piston (from the intake stroke to the compression stroke). Therefore, the larger numerical value denotes a stronger tumble air flow. In the case of the subsidiary intake air passage, the longer subsidiary[0141]intake air passage22 provides a higher tumble ratio, and in the case of thetumble control valve43, the presence of thepartitioning plate44 provides a higher tumble ratio. This is because of a construction for preventing the diffusion of flowing-in air to a position near the intake valve. Therefore, by the above-described configuration, a tumble air flow necessary for the air guide system of the present invention can be generated.
• FIG. 39 shows a tumble air flow generated in the[0142]combustion chamber13 when the piston top face is flat. An object of the tumble generating means shown in FIGS.34 to37 is to generate thetumble air flow40 having directivity in thecombustion chamber13. On the actual intake stroke, however, there exists anair flow40bwhich passes through the lower side of theintake valve27 and flows into the combustion chamber. Thisair flow40bis a flow in the direction opposite to theflow40, that is, an inverse tumble flow, which weakens the tumble flow necessary for the tumble air guide system of the present invention. It is preferable that theinverse tumble flow40bbe reduced, or the influence thereof be lessened. Sometimes, however, it is difficult to reduce theinverse tumble flow40bdepending on the shape of the intake port. If thetumble air flow40 can be generated more strongly, the influence of theinverse tumble flow40bcan be lessened.
• FIG. 39([0143]a) is a schematic view showing air flows at the bottom dead center (180 deg BTDC) of the intake stroke. Theair flow40 having directivity, which has passed through the tumble generating means, goes along the cylinder wall on the exhaust side, and the direction thereof is changed by the piston top face. When the piston top face is flat, the direction of theair flow40 is changed through about 90 degrees, preventing smooth flow. Therefore, as shown in FIG. 39(b), at the second half stage of the compression stroke (60 deg BTDC), theflows40 and40bcancel each other. To solve this problem, some consideration is needed to strengthen theair flow40.
• FIG. 40 shows a piston top face improved to strengthen the[0144]air flow40. Thefuel injection valve26 and theignition plug28 denote the positional relationship such that they are installed on the engine head.
• FIG. 40([0145]a) shows the piston top face which is curved to smoothen the flow on the piston top face. Achain line47 is parallel with the crankshaft of the engine, and achain line46 is perpendicular to thechain line47. Achain line45 lies on the same plane as that of thechain line46, and passes through the center of thefuel injection valve26. The top face of thepiston12 has aarcuate shape12awith apoint48 being the center. As a result, the outerperipheral portion12bof the piston top face is as denoted byreference numeral12c.By this shape, the direction of thetumble air flow40 is changed smoothly, preventing the flow from being weakened.
• FIG. 40([0146]b) shows the piston top face which is formed with agroove12dto prevent thetumble air flow40 from diffusing in the direction of thechain line47. Thegroove12dis parallel with thechain line46, and is provided so that theair flow40 is blown up toward thefuel injection valve26. By providing such a shape of the piston top face, the direction of theair flow40 is changed smoothly, preventing the flow from being weakened. As an effect of this improvement, an air stratum can be formed on the piston top face to prevent the fuel spray from sticking to the piston, and the fuel spray can be conveyed toward the ignition plug.
• FIG. 41 is a schematic view showing a mixing state in the[0147]combustion chamber13 of an air guide type direct injection engine in accordance with the present invention. The tumble generating means installed in theintake port21 is composed of the notchedvalve43, theshaft43a,and thepartitioning plate44.
• When the notched[0148]valve43 is closed, most of the intake air during the intake stroke passes through the upper side of thepartitioning plate44, and flows into the combustion chamber. As a result, atumble air flow40 is formed in thecombustion chamber13. The air flowing into the combustion chamber on the intake stroke on which theintake valve27 is open flows along the wall surface of combustion chamber on the side distant from thefuel injection valve26, that is, on the side of theexhaust valve29. The piston top face is formed into an arcuate shape so that theair flow40 flows smoothly, and is further formed with a groove for preventing the diffusion. By this configuration, an air stratum is formed on the piston top face, preventing the fuel from sticking thereto. Further, theair flow40 blows up toward thefuel injection valve26, and flows along the wall surface of combustion chamber on the side on which thefuel injection valve26 is installed, and the upper wall, that is, the ceiling wall of thecombustion chamber13, producing a swirl flow. Afuel spray41 is conveyed toward the ignition plug by this swirl flow. As a result, the spray can reach the plug gap of theignition plug28 regardless of the piston position, that is, regardless of the engine rotational speed. This relationship is determined only the distance from the fuel injection position to the plug gap and the spray velocity. Therefore, the stratified charge operation can be performed up to a high rotation region of 3200 rpm.
• The[0149]tumble air flow40 used in the present invention once reaches the wall surface of combustion chamber on the side of the exhaust valve in thecombustion chamber13 after going into the combustion chamber, and then returns to the intake side along the shape of the piston top face. Therefore, thefuel spray41 injected from thefuel injection valve26 installed between theintake valves27 reaches theignition plug28 through the minimum distance while being borne by the air flow. If thefuel injection valve26 is located on the side of theexhaust valve29, thefuel spray41 flows to the side of the intake valve along the piston top face, and reaches theignition plug28. Therefore, the time from when thefuel spray41 is injected to when it reaches the ignition plug is prolonged. Further, there is undesirably a possibility of the fuel sticking to the piston top face.
• In an experiment conducted by using an air guide type direct injection engine in accordance with the present invention, under the operation condition of a rotational speed of 1400 rpm and an denoted mean effective pressure Pi of 320 kPa, the injection timing (FIG. 41([0150]a)) and the ignition timing (FIG. 41(b)) at which operation can be performed stably are 70 deg BTDC and 35 deg BTDC, respectively. At this time, the time taken from injection to ignition is about 3 msec. Under the operation condition of a rotational speed of 3200 rpm and an denoted mean effective pressure Pi of 350 kPa, they are 90 deg BTDC and 30 deg BTDC, respectively. At this time, the time taken from injection to ignition is about 3.12 msec. Therefore, on the air guide type direct injection engine in accordance with the present invention, the time taken from injection to ignition is generally about 3 msec regardless of the engine rotational speed.
• The following is a description of the fuel spray using the air guide system in accordance with the present invention.[0151]
• FIG. 42 schematically shows a state of fuel spray injected from the[0152]fuel injection valve26 installed in the engine. Afuel spray41 shows a spray shape when the ambient atmosphere has the atmospheric pressure, and afuel spray41pshows a spray shape at a pressure of 0.6 Mpa. On the intake stroke and at the first half stage of the compression stroke, since the pressure in thecombustion chamber13 is nearly equal to the atmospheric pressure, the fuel spray is as denoted byreference numeral41. At the second half stage of the compression stroke, the volume of thecompression chamber13 is decreased by the rise of thepiston12, thereby increasing the pressure. Although the ambient pressure varies from 0.1 to 1.0 Mpa depending on the injection timing, the spray shape at a pressure of 0.6 Mpa is shown to identify the spray shape. The spray angle of thefuel spray41 under the atmospheric pressure is denoted by X1+X2, and the spray angle of thefuel spray41punder a pressurized condition is denoted by Y1+Y2.
• FIG. 44 shows a method for measuring the spray angle. A triangle is formed by a nozzle tip end point A of the[0153]fuel injection valve26 and spray contour points 25 mm down from the point A, and the vertical angle of this triangle is defined as the spray angle. In the case of thefuel spray41, the spray angle is an angle made by connecting points B-A-E, and in the case of thefuel spray41p,the spray angle is an angle made by connecting points C-A-D.
• Referring to FIG. 42, the[0154]fuel injection valve26 is installed in the engine at an angle A with respect to the horizontal plane. The angle A is referred to as an installation angle. The upper wall of the combustion chamber including theintake valve27 is located at an angle B with respect to the horizontal plane, and the plug gap of theignition plug28 is located at an angle C with respect to the horizontal plane. In the air guide system of the present invention, it is essential that the fuel spray reach a point around the plug gap of the ignition plug to perform the stratified charge operation. It is also essential that the fuel be prevented from sticking to the upper wall of the combustion chamber in order to reduce HC. Therefore, understanding can easily be gained if the spray contour position on the side of the ignition plug is denoted by an angle with respect to the plug gap. An angle defined by the following equation using the angle C denoting the plug gap position and an angle (X1−A) denoting the spray contour position is referred to as a top end angle J.
• Top end angleJ=(X1−A)−C  (1)
• Equation (1) denotes the top end angle under the atmospheric pressure, and the top end angle J′ under a pressurized condition is defined by the following equation.[0155]
• Top end angleJ′=(Y1−A)−C  (2)
• The top end angle can be used generally for various types of engines, not for a specific engine, because it is denoted by the spray angle, the installation angle of the fuel injection valve, and the plug gap position.[0156]
• FIG. 43 shows an experimental result for a relationship between the top end angle and the engine performance. The abscissas denote the top end angle J′ under a pressurized condition. The left-hand ordinates denote the combustion variation ratio Cpi, and the right-hand ordinates denote the exhaust concentration of hydrocarbon (HC). Cpi denotes a variation from a mean combustion pressure of about 100 to 1000 cycle. The smaller this value is, the better the combustion stability is. The top end angle of 0 degree means that the spray contour position is located at the same position as the ignition plug gap position. When the top end angle is smaller than this value, the spray contour position does not reach the plug gap, so that the combustion variation ratio Cpi increases. When the top end angle is −2 (deg) or larger, the Cpi allowable range is exceeded. At a top end angle of −2 (deg), the spray does not reach the plug gap. In the present invention, however, the spray actually reaches the plug gap because the spray is blown up toward the plug gap by the action of tumble air flow. On the other hand, a lower HC concentration is preferable. If the top end angle is large, the spray contour position undesirably reaches the upper wall of the combustion chamber and the fuel sticks thereto, so that the exhaust concentration of HC increases undesirably. It can be seen from FIG. 43 that when the top end angle is +2 (deg) or larger, the HC concentration increases, so that the fuel sticks to the upper wall of the combustion chamber. Although the definition of the top end angle does not include the angle B denoting the upper wall position of the combustion chamber, the upper limit value of the top end angle can be estimated by the exhaust behavior of HC. Therefore, in a range of top end angle from −2 to +2 (deg) under a pressurized condition, both of the combustion variation ratio Cpi and the HC exhaust concentration can be satisfied.[0157]
• Next, a method for measuring a swirl/tumble air flow will be shown. The intensity of swirl/tumble air flow is defined as a swirl ratio or a tumble ratio denoting the number of rotations of swirl or tumble air flow during the time when the engine rotates one turn. The swirl ratio Sr and the tumble ratio Tr are expressed as[0158]
• Sr=ωS/ωN, Tr=ωT/ωN
• where, ωN is an engine angular speed, ωS is a swirl flow, and ωT is a tumble flow. For example, the swirl ratio Sr=1 means that the swirl flow rotates one turn during the time when the engine rotates one turn.[0159]
• FIG. 45 shows a method for measuring the swirl air flow. The engine head (an object to be measured which produces swirl or tumble air flow) is installed on the upstream side of an[0160]impulse swirl meter450. Air is drawn by a blower, which is connected downstream so that the air amount corresponding to the engine rotational speed to be measured can flow. Thereby, a rotational torque of swirl or tumble air flow is measured by theimpulse swirl meter450. Theimpulse swirl meter450 contains ahoneycomb core451. Angular motion energy of the swirl or tumble air flow is applied to thehoneycomb core451 to rotate thehoneycomb core451. The rotational torque at this time is taken out from theshaft452, and is measured. From the measured value, the swirl intensity is calculated.
• FIG. 46 is a perspective view showing one example of a direct injection type engine using the present invention. Also, FIG. 47 is a schematic view in which FIG. 46 is viewed from above the combustion chamber.[0161]
• The[0162]groove12ais formed in the top face of thepiston12. Thisgroove12ais formed across the top face of thepiston12 from a position distant from thefuel injection valve26 to a position under thefuel injection valve26.
• An inlet of air sucked into the[0163]combustion chamber13, that is, asuction port27pis provided on the side close to thefuel injection valve26 at the upper part of thecombustion chamber13.
• The flow (denoted by a thick chain line) of air sucked into the[0164]combustion chamber13 through thesuction port27pexhibits a vertical swirl flow which goes toward the side distant from thefuel injection valve26, returns to a position under thefuel injection valve26 along thegroove12aformed in the top face of thepiston12, and further rises toward the ceiling wall of thecombustion chamber13 along the wall surface of the combustion chamber on the side on which thefuel injection valve26 is installed.
• Also, two[0165]suction ports27pfor sucking air are formed at the upper part of thecombustion chamber13, and thefuel injection valve26 is installed between the twosuction ports27p.
• The axis of the[0166]fuel injection valve26 is inclined toward a position under theignition plug28 installed at the upper part of the combustion chamber.
• The ignition plug[0167]28 slightly shifts from the center of the upper part of the combustion chamber to the side of anexhaust valve30. The reason for this is that a distance suitable for carrying the fuel from thefuel injection valve26 to theignition plug28 is ensured. If theplug28 is located at the center of the upper part of the combustion chamber depending on the type of engine, the distance becomes too short, so that the fuel may pass through the plug earlier than the normal ignition timing.
• Further, the axis of the[0168]fuel injection valve26 is arranged so as to be perpendicular to the axis of a connecting pin for connecting the connectingrod14 to thepiston12, with the result that thegroove12ain the top face of the piston is formed at right angles with respect to ahole14cfor inserting the connecting pin.
• This has an effect of keeping a balance of mass of the piston. Also, this has an advantage that even if the groove is formed, the temperature distribution in the piston does not become ill-balanced so much.[0169]
• Air flows[0170]40L and40R entering thecombustion chamber13 through the twosuction ports27pgo toward the opposite wall so that both the air flows tend to go inside, and join into oneflow40cwhen they collide with the wall.
• After joining, the air flow moves downward along the wall, and is guided to a position under the[0171]fuel injection valve26 by a pair of wall surfaces (denoted by broken lines in FIG. 47) forming thegroove12aof thepiston12.
• Then, the air flow collides with the wall on the side of the[0172]fuel injection valve26 and goes upward, and is guided by the ceiling of thecombustion chamber13, the twointake valves27,27, or the twoair flows40L and40R going into the combustion chamber through the twosuction ports27p,27p.Thereupon, the air flow passes between the twoair flows40L and40R, going from thefuel injection valve26 to the ignition plug, and is then absorbed by theair flow40c.
• The[0173]fuel injection valve26 injects fuel into the flow from thefuel injection valve26 to theignition plug28 in such atumble air flow40, and the fuel is carried from thefuel injection valve26 to theignition plug28 by the air flow.
• With this method, the distance through which fuel is carried is short, so that there is less possibility for the fuel to stick to the wall surface of combustion chamber and the like.[0174]
• In particular, the piston is isolated by two air strata, a stratum of air flowing to the side of the[0175]fuel injection valve26 by being guided by thegroove12aand a stratum of air flowing from thefuel injection valve26 to theplug28. Therefore, the fuel scarcely reaches thepiston12.
• In the embodiment with the above-described configuration, an experiment has revealed that the stratified charge operation by the tumble guide can be performed not only in the region of high load and high rotational speed as described above but also under a severe condition such as the cranking time or the cold start time.[0176]
• Since the stratified charge operation can be performed at the cranking time or the cold start time, ignition can be accomplished surely from the first detonation, and the first misfire at the start time does not occur at all. As a result, the harmful components of exhaust gas can be reduced.[0177]
Industrial Applicability
• The control method for an internal combustion engine in accordance with the present invention has an excellent effect such that fuel does not stick to the piston at the time of stratified charge combustion, so that exhaust gas can be purified, and also a mixture can be mixed uniformly at the time of homogeneous operation, so that the output can be increased. Therefore, the method is useful for the internal combustion engine, injection valve, and other similar devices, and also is suitable for the stratified charge lean operation at the time of high rotational speed of 120 km/h or 3200 rpm and the increase in fuel efficiency.[0178]

Claims (23)

1. A cylinder injection type internal combustion engine comprising:

a combustion chamber into which air is sucked;

a fuel injection valve for injecting fuel directly into said combustion chamber; and

a piston for changing the volume of said combustion chamber,

characterized in that said piston has a face allowing the flow of air to go from the side of the wall surface in said combustion chamber opposite to said fuel injection valve to just under said fuel injection valve, and

a stratum of the sucked air or a stratum of air flow is interposed between a fuel spray injected from said fuel injection valve and the wall surface in said combustion chamber on the installation side of said fuel injection valve and between said fuel spray and the top face of said piston.

2. A cylinder injection type internal combustion engine comprising a fuel injection valve for injecting fuel directly into a combustion chamber of said internal combustion engine,

characterized in that penetration of a fuel spray injected from said fuel injection valve into said combustion chamber is set to be shorter than a distance between the top face of a piston reciprocating in said combustion chamber and a fuel discharge port of said fuel injection valve during a period of time from the start of injection to the completion of injection of fuel.

3. A cylinder injection type internal combustion engine comprising a fuel injection valve for injecting fuel directly into a combustion chamber of said internal combustion engine,

characterized in that said fuel injection valve is formed so that the penetration of a fuel spray 3.8 msec after the injection of fuel to the atmosphere of the atmospheric pressure is 60 mm or shorter.

4. A cylinder injection type internal combustion engine comprising a fuel injection valve for injecting fuel directly into a combustion chamber of said internal combustion engine,

characterized in that said fuel injection valve is formed so that a fuel spray with a Zauter mean particle size of 20 μm or smaller is injected.

5. The cylinder injection type internal combustion engine according toclaim 3 or4, characterized in that said fuel injection valve has an atomizer formed by lapping a plurality of plates having a circular or polygonal hole.

6. A cylinder injection type internal combustion engine, comprising:

a combustion chamber for said internal combustion engine into which air is sucked through an intake valve;

a fuel injection valve for injecting fuel directly into said combustion chamber;

swirl flow generating means for generating a swirl air flow in said combustion chamber; and

operation condition detecting means for detecting the operation condition of said internal combustion engine,

characterized in that said internal combustion engine has a control unit for supplying a fuel injection valve driving signal to said fuel injection valve so that fuel is injected at the second half stage of the compression stroke when the detected operation condition is at a low load.

7. A cylinder injection type internal combustion engine comprising:

a combustion chamber of said internal combustion engine, into which air is sucked through an intake valve;

a fuel injection valve for injecting fuel directly into said combustion chamber;

swirl flow generating means for generating a swirl air flow in said combustion chamber; and

operation condition detecting means for detecting the operation condition of said internal combustion engine,

characterized in that said internal combustion engine has a control unit for supplying a fuel injection valve driving signal to said fuel injection valve so that fuel is injected on the intake stroke when the detected operation state is at a medium load.

8. A cylinder injection type internal combustion engine comprising:

a combustion chamber of said internal combustion engine, into which air is sucked through an intake valve;

a fuel injection valve for injecting fuel directly into said combustion chamber; and

operation condition detecting means for detecting the operation condition of said internal combustion engine,

characterized in that said internal combustion engine has a control unit for supplying a fuel injection valve driving signal to said fuel injection valve so that fuel is injected for a period of time when the intake air velocity is lower than the spray velocity on the intake stroke when the detected operation condition is at a high load.

9. The cylinder injection type internal combustion engine according toclaim 8, characterized in that

said fuel injection valve has an atomizer formed by lapping a plurality of plates having a circular or polygonal hole, and

said control unit supplies a fuel injection valve driving signal to said fuel injection valve so that fuel is injected a plurality of times before and after the timing at which said intake valve is fully opened.

10. A cylinder injection type internal combustion engine comprising:

an upstream swirl type fuel injection valve for injecting fuel directly into a combustion chamber of said internal combustion engine; and

operation condition detecting means for detecting the operation condition of said internal combustion engine,

characterized in that said internal combustion engine has a control unit for supplying a fuel injection valve driving signal to said fuel injection valve so that fuel is injected at a time for a period of time when the intake air velocity is higher than the spray velocity on the intake stroke when the detected operation condition is at a high load.

11. A control method for a cylinder injection type internal combustion engine, characterized in that when the operation condition of said internal combustion engine is at a low load,

a swirl air flow is generated in a combustion chamber,

fuel is injected at the first half stage of the compression stroke, and

a rich mixture stratum is formed inside said swirl air flow,

whereby stratified charge lean operation is performed.

12. A control method for a cylinder injection type internal combustion engine, characterized in that when the operation condition of said internal combustion engine is at a medium load,

a swirl air flow is generated in a combustion chamber,

fuel is injected on the intake stroke, and

a mixture with a homogeneous concentration is generated in said combustion chamber by said swirl air flow,

whereby homogeneous lean operation is performed.

13. A control method for a cylinder injection type internal combustion engine, characterized in that when the operation condition of said internal combustion engine is at a high load,

fuel having an amount capable of achieving a stoichiometric air-fuel ratio is injected for a period of time when the intake air velocity is lower than the spray velocity on the intake stroke, and a mixture with a homogeneous concentration is generated in the combustion chamber by intake air,

whereby homogeneous stoichiometric operation is performed.

14. A fuel injection valve for injecting fuel directly into a combustion chamber of an internal combustion engine,

characterized in that a fuel spray injected from said fuel injection valve has a penetration of 60 mm or shorter 3.8 msec after the time when fuel is injected to the atmosphere of the atmospheric pressure.

15. A fuel injection valve for injecting fuel directly into a combustion chamber of an internal combustion engine,

characterized in that the spray particle size of fuel injected from said fuel injection valve is 20 μm or smaller in terms of Zauter mean particle size.

16. The fuel injection valve according toclaim 14 or15,

characterized in that said fuel injection valve has an atomizer formed by lapping a plurality of plates having a circular or polygonal hole through which fuel goes to a fuel ejection portion of said fuel injection valve.

17. A cylinder injection type internal combustion engine comprising:

a combustion chamber into which air is sucked;

a fuel injection valve for injecting fuel directly into said combustion chamber; and

a piston for changing the volume of said combustion chamber,

characterized in that a groove is formed in the top face of said piston,

said groove being formed across the top face of said piston from a position distant from said fuel injection valve to a position under said fuel injection valve,

an inlet of air sucked into said combustion chamber is provided on the side close to said fuel injection valve at the upper part of said combustion chamber, and

the flow of air sucked into said combustion chamber through said inlet exhibits a swirl flow which goes toward the side distant from said fuel injection valve, returns to a position under said fuel injection valve along said groove formed in the top face of said piston, and further rises toward the ceiling wall of said combustion chamber along the wall surface of said combustion chamber on the side on which said fuel injection valve is installed.

18. The cylinder injection type internal combustion engine according toclaim 17, characterized in that valve means which forms a throttle for increasing the flow velocity of intake air is provided on the upstream side of said air inlet provided at the upper part of said combustion chamber.

19. A cylinder injection type internal combustion engine comprising:

a combustion chamber into which air is sucked;

a fuel injection valve for injecting fuel directly into said combustion chamber; and

a piston for changing the volume of said combustion chamber,

characterized in that a cavity is formed in the top face of said piston,

said cavity has convex portions on the side distant from said fuel injection valve and on the side close to said fuel injection valve, and has a deep concave portion at an intermediate portion between said two convex portions,

an inlet of air sucked into said combustion chamber is provided on the side close to said fuel injection valve at the upper part of said combustion chamber, and

the flow of air sucked into said combustion chamber through said inlet exhibits a swirl flow which goes toward the side distant from said fuel injection valve, returns to a position under said fuel injection valve along said cavity formed in the top face of said piston, and further rises toward the ceiling wall of said combustion chamber along the wall surface of said combustion chamber on the side on which said fuel injection valve is installed.

20. A cylinder injection type internal combustion engine comprising:

a combustion chamber into which air is sucked;

a fuel injection valve for injecting fuel directly into said combustion chamber; and

a piston for changing the volume of said combustion chamber,

characterized in that an inlet of air sucked into said combustion chamber is provided on each side of said fuel injection valve installed at the upper part of said combustion chamber, and

the flow of air sucked into said combustion chamber through said two inlets exhibits a swirl flow which goes toward the side distant from said fuel injection valve, returns to a position under said fuel injection valve along the top face of said piston, and further rises toward the ceiling wall of said combustion chamber along the wall surface of said combustion chamber on the side on which said fuel injection valve is installed.

21. A cylinder injection type internal combustion engine comprising:

a combustion chamber into which air is sucked;

a fuel injection valve for injecting fuel directly into said combustion chamber; and

a piston for changing the volume of said combustion chamber,

characterized in that two suction ports for sucking air are formed at the upper part of said combustion chamber, and said fuel injection valve is installed between said two suction ports,

the axis of said fuel injection valve is inclined toward a position under an ignition plug installed at the upper part of said combustion chamber, and

the flow of air sucked into said combustion chamber through said suction ports exhibits a swirl flow which goes toward the side distant from said fuel injection valve, returns to a position under said fuel injection valve along the top face of said piston, and further rises toward the ceiling wall of said combustion chamber along the wall surface of said combustion chamber on the side on which said fuel injection valve is installed.

22. A cylinder injection type internal combustion engine comprising:

a combustion chamber into which air is sucked;

a fuel injection valve for injecting fuel directly into said combustion chamber; and

a piston for changing the volume of said combustion chamber,

characterized in that two suction ports for sucking air are formed at the upper part of said combustion chamber, and said fuel injection valve is installed between said two suction ports,

the axis of said fuel injection valve is arranged so as to be perpendicular to the axis of a connecting rod or a piston pin of said engine, and

the flow of air sucked into said combustion chamber through said suction ports exhibits a swirl flow which goes toward the side distant from said fuel injection valve, returns to a position under said fuel injection valve along the top face of said piston, and further rises toward the ceiling wall of said combustion chamber along the wall surface of said combustion chamber on the side on which said fuel injection valve is installed.

23. The cylinder injection type internal combustion engine according to any one ofclaims 17 to22, characterized in that the fuel injection timing is set at 3.0 msec±0.5 msec before the ignition timing.

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